Production of organic acid esters of cellulose



Patented Feb. 3, 1953 PRODUCTION OF ORGANIC ACID ESTERS OF CELLULOSEBlanche BJWhite, Summit, and Peter Blackman,

Westfield, N. J., assignors to Celanese Corporation of.America, NewYork, N. Y., a corporation of Delaware 'No Drawing.

Application April 13, 1951,

Serial No. 220,976

14 Claims.

This invention-relates to the production of organic acid esters ofcellulose and relates more particularly to an improved process for theproduction of organic acid esters of cellulose which may be carried outin a continuous manner.

In the production of organic acid esters of cellulose by theesterification of a cellulosic material, it is customary to pretreat thecellulosic material before esterification to increase its reactivity andthereby reduce the esterification time. To enable the production of theorganic acid esters of cellulose to be carried out in a continuousmanner, the pretreatment should require only a relatively short periodof time, In addition, the pretreatment should increase the reactivity ofthe cellulosic material to a point where the esterification thereof willbe completed rapidly.

It is an important object of this invention to provide a process for theproduction of organic acid esters of cellulose which will fulfill theforegoing requirements and which may be carried out in a continuousmanner.

.A further object of this invention is to provide a novel process forpretreating cellulosic material which may be carried out in a relativelyshort period of time and which will render said cellulosic materialhighly reactive.

Other objects of this invention will be apparent from the followingdetailed description and claims.

According to the present invention, a cellulosic material is pretreatedwith a mixture of alower aliphatic acid and an acid celluloseesteri'fication catalyst for the cellulosic material, said mixturecontaining from about 75 to 25 parts by weight of the acid celluloseesterification catalyst for each 100 parts by Weight of the loweraliphatic acid, in the presence of from about 8 to 20 parts by weight ofwater for each 109 parts by weight of the lower aliphatic acid. Theamount of water which must be present during the pretreatment may be inor may be added to the cellulosic ma terial before the pretreatmentbegins, or it may be included in the pretreatment mixture, or a portionof the water may be in or may be added to the cellulosic material beforethe pretreatment begins and the remainder of the water may be includedin the pretreatment mixture. ferred, however, to employ for thepretreatment a cellulosic material containing at least about 4 parts byweight of water for each 100 parts by weight of the cellulosic material,since a cellulosic material containing a smallerquantity of water willnot be rendered as reactive by the pretreatment as a cellulosic materialcontaining at least this minimum quantity of water.

The .best results and the most highly reactive cellulosic materials areobtained when the materials in the pretreatment mixture are employed inthe ratio specified above and there is present during the pretreatmentfrom about 4 to '7 parts by weight of water foreach 100 parts by weightof the cellulosicmaterial. .In the case when this quantity of water,based on the cellulosic material, is present during the pretreatment,there should be employed from about 35 to 45 parts by weight of thelower aliphatic acid and from about 4 to 8 parts by weight of the acidcellulosic esterificationcatalyst for each 100 parts by weight of thecellulosic material to maintain the proper ratio of materials during thepretreatment.

The time required for the pretreatment of the cellulosic material underthe conditions and with the materials specified is relatively short andthe single stage of pretreatment yields a cellulosic material having anextremely high reactivity which may be esterified rapidly.

The process of the present invention may be applied to any suitablecellulosic material, suchas cotton linters, or wood pulps or the likefrom It is prewhich the lignin, ,pentosan, resins, and similarconstituents have been removed, as for example,

purified sulfite pulp, sulfate pulp or soda pulp.

In addition, there may be employed cellulosic material derived fromother sources such as bamboo, reeds, jute, esparto, straws such aslinseed and hempseed straw, grasses, peanut hulls, bark, etc, Thecellulosic material pretreated may be .in the form of a mass of loosefibers, or in a form of a sheet, strip or board.

Any of the lower aliphatic acids including formic, acetic, propionic andbutyric acids, as well as mixtures thereof, may be employed for the.pretreatment of the cellulosic material. Similarly, any of the acidcellulose esterification catalysts may be employed with the loweraliphatic acid during the pretreatment, but is is preferred to employsulfuric acid for this purpose since it is the cheapest and leasthazardous catalyst which produces a cellulosic material having a highreactivity in a short period of time.

The pretreatment mixture may be applied to the cellulosic material inany desired manner. For example, it may be sprayed or rolled onto thecellulosic material, or, when the cellulosic material is in the form ofa sheet, strip orlaoard, the pretreatment mixture may be applied theretofrom a perforated or slotted conduit extending the full width of thesheet, strip or board. In pretreating cellulosic material in the form ofa mass of loose fibers, vigorous agitation should be provided during theapplication of the pretreatment mixture and during the first portion ofthe pretreatment period. to insure a uniform distribution of thepretreatment mixture through the entire mass of material. Agitation ofthe cellulosic material should be continued during the entirepretreatment period, although less vigorous agitation may be employedduring the latter stages thereof, it having been found that continuousagitation produces a more highly reactive cellulosic material ascompared with a cellulosic material that is permitted to stand withoutagitation during a portion of the pretreatment period.

The temperature employed for the pretreatment is not critical and mayrange from about .20 to 50 C. A period of at least about 5 minutes orpreferably between about 5 and 40 minutes should be allowed for thepretreatment to obtain a cellulosic material having the highestreactivity.

The pretreated cellulosic material is esterified with an organic acidanhydride, preferably employing an esterification mixture which containsadditional quantities of lower aliphatic acid and which may also containadditional quantities of the esterification catalyst. The esterificationmixture is advantageously cooled to freeze at least a portion of thelower aliphatic acid therein to prevent an excessive rise in temperaturewhen the highly reactive cellulosic material is first contactedtherewith. Esterification proceeds rapidly .and is completed in about 15to 30 minutes, or

' ably after the addition of a further quantity of water, may bepermitted to hydrolyze or ripen to impart the desired solubilitycharacteristics thereto. The organic acid ester of cellulose may then beprecipitated from the dope, washed to free it from acids or otherimpurities, stabilized if necessary, washed again and finally dried.When organic acid esters of cellulose are prepared in accordance withthe process of this invention, it is possible to carry out both thepretreatment and esterification on a continuous rather than on a batchbasis, since the time required for both steps is sufficiently short torender a continuous process feasible.

Our invention will now be described specifically in connection with theproduction of cellulose acetate, which is commercially the mostimportant organic acid ester of cellulose at the present time. It may,however, also be employed for the production of other organic acidesters of cellulose such as, for example, the lower aliphatic acidesters of cellulose including cellulose propionate, cellulose butyrate,cellulose acetate propionate and cellulose acetate butyrate bysubstituting the corresponding organic acid anhydrides for the aceticanhydride employed in the production of cellulose acetate.

The following examples are given to illustrate this invention further.

Example I Onto 100 parts by weight of cotton linters containing 6 partsby weight of water, there is sprayed a mixture containing 40 parts byweight of acetic acid and 6 parts by weight of sulfuric acid, and thecotton linters are stirred with rapid and efiicient agitation for 15minutes. The pretreated cotton linters are then esterified with anesterification mixture containing 250 parts by weight of aceticanhydride, 370 parts by weight of acetic acid and 7 parts by weight ofsulfuric acid, which esterification mixture has been cooled to atemperature of 0 C. Esterification is complete in 16 minutes asevidenced by the clearing of the dope.

Example II Onto 100 parts by weight of cotton linters containing 6 partsby weight of water, there is sprayed a mixture containing 35 parts byweight of acetic acid and 6 parts by weight of sulfuric acid, and thecotton linters are stirred with rapid and efficient agitation for 6minutes. The pre treated cotton linters are then esterified with anesterification mixture containing 250 parts by weight of aceticanhydride, 330 parts by weight of acetic acid and 7 parts by weight ofsulfuric acid, which esterification mixture has been cooled to 0 C.Esterification is complete in 16 minutes as evidenced by the clearing ofthe dope.

Example III Onto 100 parts by weight of cotton linters containing 12parts by weight of water, there is sprayed a mixture containing parts byweight of acetic acid and 12 parts by weight of sulfuric acid, and thecotton linters are stirred with rapid and efficient agitation for 6minutes. The pretreated cotton linters are then esterified with anesterification mixture containing 290 parts by weight of aceticanhydride and 240 parts by weight of acetic acid, which esterificationmixture has been cooled to 0 C. Esterification is complete in 16 minutesas evidenced by the clearing of the dope.

Example I V Onto parts by weight of cotton linters containing 6 parts byweight of water, there is sprayed a mixture containing 4.0 parts byweight of acetic acid and 6 parts by weight of sulfuric acid, and thecotton linters are stirred slowly in a paddle mixer for 35 minutes. Thepretreated cotton linters are then esterified with an esterificationmixture containing 250 parts by weight of acetic anhydride, 330 parts byweight of acetic acid, and '7 parts by weight of sulfuric acid, whichesterification mixture has been cooled to 6 C. Esterification iscomplete in 21 minutes as evidenced by the clearnig of the dope.

It is to be understood that the fore oing detailed description is givenmerely by way of i llustration and that many variations may be madetherein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by LettersPatent is:

1. A process for the production of "organic acid esters of cellulosefrom cellulosic material, which comprises pretreating cellulosicmaterial with a mixture of a lower aliphatic acid and an acid celluloseesterification catalyst, said mixture containing from about 7.5to-25parts by wei'ghtfof the 'esterification catalyst -'for each 100 parts-byweight of the lower aliphatic acid, injthe presence" of from about 8 toparts by weight of water for eachlOO parts by weight of the loweraliphatic acid, and esterifying the pretreated cellulosic material withan organic acid anhydride.

2. A process for the production of organic acid esters of cellulose fromcellulosic material, which comprises pretreating acellulosic'materialfor "a period of at least about 5 minutes with amixture of a lower aliphatic acid and an acid cellulose esterificationcatalyst, said mixture containing fromabout 7.5 to parts by weight oftheesterification catalyst for each 100 parts by weight" of theioweraliphatic'acid, in the presence of j -fro'm" about -8-to"20 parts byweighed v'v'ait'erfore'ach lflfl parts "by weight of the low'eraliphatic acid, and esterifying the pretreated cellulosic material withan organic acid anhydride.

3. A process for the production of organic acid esters of cellulose fromcellulosic material, which comprises pretreating a cellulosic materialcontaining at least about 4 parts by weight of water for each 100 partsby weight of the cellulosic material with a mixture of a lower aliphaticacid and an acid cellulose esterification catalyst, said mixturecontaining from about 7.5 to 25 parts by weight of the esterificationcatalyst for each 100 parts by Weight of the lower aliphatic acid, inthe presence of from about 8 to 20 parts by Weight of water for each 100parts by weight of the lower aliphatic acid, and esterifying thepretreated cellulosic material with an organic acid anhydride.

4. A process for the production of organic acid esters of cellulose fromcellulosic material, which comprises pretreating a cellulosic materialwith a mixture of a lower aliphatic acid and an acid celluloseesterification catalyst, said mixture containing from about 4 to 8 partsby weight of the esterification catalyst, and from about to parts byweight of the lower aliphatic acid for each 100 parts by weight of thecellulosic material, in the presence of from about 4 to 7 parts byweight of water for each 100 parts by weight of the cellulosic material,and esterifying the pretreated cellulosic material with an organic acidanhydride.

5. A process for the production of lower aliphatic acid esters ofcellulose from cellulosic material, which comprises pretreating acellulosic material with a mixture of acetic acid and sulfuric acid,said mixture containing from about 7.5 to 25 parts by weight of sulfuricacid for each 100 par-ts by weight of acetic acid, in the presence offrom about 8 to 20 parts by weight of water for each 100 parts by weightof the acetic acid, and esterifying the pretreated cellulosic materialwith a lower aliphatic acid anhydride.

6. A process for the production of lower aliphatic acid esters ofcellulose from cellulosic material, which comprises pretreating acellulosic material for a period of between about 5 and 40 minutes witha mixture of acetic acid and sulfuric acid, said mixture containing fromabout 7.5 to 25 parts by Weight of sulfuric acid for each 100 parts byweight of acetic acid, in the presence of about 8 to 20 parts by weightof water for each partsby weight of the acetic acid and,

esterifying the pretreated cellulosic material with -ofacetic-acidahdsulfuric acid, said mixture containi'ri'g-'-froin about 7.5 to 25 partsby weight of sulfuric acid for each 100 parts by weight of aceticanagrams presence-of from about 8 to 20 parts by wei'ght of water'for'each 100 parts by weight of the acetic acid, and esterifying thepretreated cel lulosic material with a lower aliphatic acid anhy dride,

8. A process for the production of lower aliphatic acid esters ofcellulose from cellulosic material, which comprises pretreating acellulosic materialwitha mixture of aceueasia and silk" acid;saidmixturecontaining froih ab'o parts by-weight of*sulfuric-acid an"df'rom--ab'o"ut 35 to 45 parts by weight of acetic acid for each 100parts by weight of the cellulosic material, in the presence of fromabout 4 to 7 parts by weight of water for each 100 parts by weight ofthe cellulosic material, and esterifying the pretreated cellulosicmaterial with a lower aliphatic acid anhydride.

9. A process for the production of lower aliphatic acid esters ofcellulose from cellulosic material, which comprises pretreating acellulosic material containing at least about 4 parts by I weight ofwater for each 100 parts by weight of the cellulosic material for aperiod of between about 5 and 40 minutes with a mixture of acetic 'acidand sulfuric acid, said mixture containing from about 4 to 8 parts byweight of sulfuric acid and from about 35 to 45 parts by weight ofacetic acid for each 100 parts by weight of the cellulosic material, inthe presence of from about 4 to 7 parts by weight of water for each 100parts by weight of the cellulosic material, and esterifying thepretreated cellulosic material with a lower aliphatic acid anhydride.

10. A process for the production of cellulose acetate from cellulosicmaterial, which comprises pretreating a cellulosic material with amixture of acetic acid and sulfuric acid, said mixture containing fromabout 7.5 to 25 parts by weight of sulfuric acid for each 100 parts byweight of acetic acid, in the presence of from about 8 to 20 parts byweight of water for each 100 parts by weight of the acetic acid, andesterifying the pretreated cellulosic material with acetic anhydride.

.11. A process for the production of cellulose acetate from cellulosicmaterial, which comprises pretreating a cellulosic material for a periodof between about 5 and 40 minutes with a mixture of acetic acid andsulfuric acid, said mixture containing from about 7.5 to 25 parts byweight of sulfuric acid for each 100 parts by weight of acetic acid, inthe presence of from about 8 to 20 parts by weight of water for each 100parts by weight of the acetic acid, and esterifying the pretreatedcellulosic material with acetic anhydride.

12. A process for the production of cellulose acetate from cellulosicmaterial, which comprises pretreating a, cellulosic material containingat least about 4 parts by weight of water for each 100 parts by weightof the cellulosic material with a mixture of acetic acid and sulfuricacid, said mixture containing from about 7.5 to 25 parts by weight ofsulfuric acid for each. 100

parts by weight of acetic acid, in the presence of from about 8 to 20parts by weight of water for each 100 parts by weight of the aceticacid, and esterifying the pretreated cellulosic material with withacetic anhydride.

13. A process for the production of cellulose acetate from cellulosicmaterial, which comprises pretreating a cellulosic material with amixture of acetic acid and sulfuric acid, said mixture containing fromabout 4 to 8 parts by weight of sulfuric acid and from about 35 to 45parts by weight of acetic acid for each 100 parts by weight of thecellulosic material in the presence of from about 4 to '7 parts byweight of water for each 100 parts by weight of the cellulosic material,and esterifying the pretreated cellulosic material.

14. A process for the production of cellulose acetate from cellulosicmaterial, which comprises pretreating a cellulosic material containingat least about 4 parts by weight of water for each 100 parts by weightof the cellulosic material for a period of between about and 40 minuteswith a mixture of acetic acid and sulfuric acid, said mixture containingfrom about 4 to 8 parts by weight of sulfuric acid and from about toparts by weight of acetic acid for each parts by weight of thecellulosic material, in the presence of from about 4 to '7 parts byweight of water for each 100 parts by weight of the cellulosic material,and esterifying the pretreated cellulosic material.

BLANCHE B. WHITE.

PETER BLACKMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,389,250 Koetschet et al Aug.30, 1921 1,425,581 Esselen et a1 Aug. 15, 1922 2,110,642 Auden et a1Mar. 8, 1938 2,115,735 Malm May 3, 1938 2,342,416 Malm Feb. 22, 1944

1. A PROCESS FOR THE PRODUCTION OF ORGANIC ACID ESTERS OF CELLULOSE FORCELLULOSIC MATERIAL, WHICH COMPRISES PRETREATING CELLULOSIC MATERIALWITH A MIXTURE OF A LOWER ALIPHATIC ACID AND AN ACID CELLULOSEESTERIFICATION CATALYST, SAID MIXTURE CONTAINING FROM ABOUT 7.5 TO 25PARTS BY WEIGHT OF THE ESTERIFICATION CATALYST FOR EACH 100 PARTS BYWEIGHT OF THE LOWER ALIPHATIC ACID, IN THE PRESENCE OF FROM ABOUT 8 TO20 PARTS BY WEIGHT OF WATER FOR EACH 100 PARTS BY WEIGHT OF THE LOWERALIPHATIC ACID, AND ESTERIFYING THE PRETREATED CELLULOSIC MATERIAL WITHAN ORGANIC ACID ANHYDRIDE.